The present invention concerns solid alkali metal silicate comprising sodium and potassium. The silicate also contains from about 1 to about 5% by weight of K.sub.2 O and has a water content from about 17 to about 25% by weight. The invention also concerns a method of its preparation, its use and cleaning compositions containing such silicate.
Sodium metasilicate, i.e. sodium silicate having a molar ratio SiO.sub.2 :Na.sub.2 O of about 1, is frequently used in cleaning products such as washing and dishwasher agents. The silicate inhibits corrosion on glass, glazing and metal parts and also functions as an alkali generating agent. Generally, granules of pentahydrate are used, which granules dissolve quickly in water. However, many products contain metasilicate in such a high amount that a very high alkalinity is obtained, which renders the products corrosive and unpleasant to handle.
Less alkalinity but the same protection against corrosion can be obtained by the use of sodium silicates having a higher molar ratio SiO.sub.2 :Na.sub.2 O, for example disilicates whose molar ratio is about 2. For use in high concentrated cleaning products it is highly desirable that the silicate has as high bulk density as possible. A spray dried powder of disilicate may be brought to granules with suitable size and high bulk density by compacting, which for example is shown in U.S. Pat. No. 3,835,216. However, such compacted disilicates dissolve too slowly in water to be useful in commercial products in practice.